What Is a ‘Long-Range Attack’ in PoS?

A long-range attack is a unique PoS attack where an attacker uses their old, non-staked private keys to create an alternative chain history from the genesis block or a very early point. Since the original stake is no longer active, the attacker faces no slashing penalty.

This is a significant threat to PoS networks, especially after a protocol upgrade, and requires specific defense mechanisms like checkpointing or social consensus.